1. Field of Invention
The present invention relates generally to the field of wireless communication and data networks. More particularly, in one exemplary aspect, the present invention is directed to methods and apparatus for flexible modes of operation in a transceiver.
2. Description of Related Technology
Universal Mobile Telecommunications System (UMTS) is an exemplary implementation of a “third-generation” or “3G” cellular telephone technology. The UMTS standard is specified by a collaborative body referred to as the 3rd Generation Partnership Project (3GPP). The 3GPP has adopted UMTS as a 3G cellular radio system targeted for inter alia European markets, in response to requirements set forth by the International Telecommunications Union (ITU). The ITU standardizes and regulates international radio and telecommunications. Enhancements to UMTS will support future evolution to fourth generation (4G) technology.
A current topic of interest is the further development of UMTS towards a mobile radio communication system optimized for packet data transmission through improved system capacity and spectral efficiency. In the context of 3GPP, the activities in this regard are summarized under the general term “LTE” (for Long Term Evolution). The aim is, among others, to increase the maximum net transmission rate significantly in future, namely to speeds on the order of 300 Mbps in the downlink transmission direction and 75 Mbps in the uplink transmission direction. To improve transmission over the air interface to meet these increased transmission rates, new techniques have been specified.
The current LTE specification describes several multiple access methods. For the downlink transmission direction, OFDMA (Orthogonal Frequency Division Multiple Access) in combination with TDMA (Time Division Multiple Access) will be used. Uplink data transmission is based on SC-FDMA (Single Carrier Frequency Division Multiple Access) in combination with TDMA. Further, LTE is expected to support full-duplex FDD, half-duplex FDD and TDD (time division duplexing).
FIG. 1A illustrates the aforementioned full-duplex FDD, half-duplex FDD and TDD according to the prior art. Full-duplex FDD uses two separate frequency bands for uplink 122 and downlink 120 transmissions, and both transmissions can occur simultaneously. Unfortunately, full-duplex operation has a fixed amount of bandwidth (typically symmetrically divided between uplink 122 and downlink 120) allocated for data streams. Dynamically changing loads on the uplink 122 and downlink 120 data streams waste spectral resources; even during periods of low data rate, the bandwidth must remain assigned.
Furthermore, full-duplex FDD requires a duplex filter in order to separate the received waveform from the transmitted waveform. This duplex filter is “expensive” in terms of battery consumption, power amplifier cost and radio frequency sensitivity, especially when viewed from the perspective of a UE (e.g., mobile device or handset) manufacturer.
Unlike FDD, TDD uses the same frequency band for transmission in both uplink 122 and downlink 120. Within a given time frame, the direction of transmission is switched alternatively between the downlink 120 and uplink 122. TDD systems have the benefit that receive and transmit are not necessarily scheduled symmetrically, and can support uplink/downlink data variation more flexibly than Full-Duplex FDD. Furthermore, TDD operation does not require a duplex filter because receive and transmit are on the same frequency band. The primary challenge for time-divided systems such as TDMA and TDD is the isolation of one time slot from another, necessary to minimize interference. Timing management is handled by shifting transmission time to match the required time of arrival. The 3GPP has standardized a variable timing advance (TA) to control time synchronization between UE and base stations. Within a time slot, the amount of time necessary to maintain isolation is wasted as it cannot be used for data transmission/reception, therefore lower switching rates are desirable.
Half duplex FDD uses two separate frequency bands for uplink 122 and downlink 120 transmissions, similar to full-duplex FDD, but uplink and downlink transmissions are non-overlapping in time. The main benefit of half duplex FDD compared to full-duplex FDD is that the FDD duplex filter can be replaced by a relatively simple switch for transmit/receive separation. Unfortunately, half-duplex FDD operation must be scheduled in the same manner as a time-divided (e.g., TDD) system. Furthermore, half-duplex FDD suffers from spectral inefficiency due to incomplete frequency band usage (only one of the uplink 122 or downlink 120 bands is active for a UE at any given point). However the advantages of half-duplex FDD operation, as viewed from an operational standpoint of the base station, include allowing multiple UEs to time-share uplink and downlink resources. Accordingly, half-duplex FDD operation can be implemented on FDD networks for managing large groups of asymmetric data requirements, in a manner similar to TDD networks.
Half-duplex FDD operation in LTE systems is further described in Tdoc R1-080598, “Way forward for half duplex”, Ericsson et al., 14-18 Jan. 2008, and Tdoc R1-080534, “Half Duplex FDD in LTE”, Ericsson, Nokia, Nokia Siemens Networks, 14-18 Jan. 2008, each of which is incorporated herein by reference in its entirety. In current implementations of half duplex operation in LTE networks, sub frames are assigned to a UE for uplink or downlink transmission as a result of the scheduler operation in eNodeB. The eNodeB scheduler ensures that a UE is not transmitting and receiving in the same subframe. Accordingly, the UE is typically prepared to receive downlink (DL) transmissions in all subframes, and uplink (UL) transmissions are explicitly assigned through what is known as a scheduling grant.
Due to the TDMA component of the LTE multiple access schemes in the UL and DL, so-called timing advance (TA) adjustments for the uplink transmissions are utilized. These adjustments are implemented using a signal from a UE that arrives at the base transceiver station according to the determined frame/subframe timing, so that it does not interfere with the transmission of other UEs. A timing advance value corresponds to the length of time a UE has to advance its timing of UL transmission, and is sent by the eNodeB to the UE according to the perceived propagation delay of UL transmissions.
FIG. 1B is a detail of the prior art half duplex scheme shown in FIG. 1A, with a chronology of the uplink and downlink transmissions labeled 130, 132, and 134. As shown, the current proposal for implementation of a DL-UL switch specifies that, for a UE receiving in sub-frame n 130 and transmitting on sub-frame n+1 134, a reserved period 136 for UE switching between receive and transmit shall be provided at the end of the downlink sub-frame 130 preceding the sub-frame 134 in which the UE is required to transmit. In a subframe 130 allocated for DL transmission directly before an UL transmission is due, the time available for the actual data transmission is thus reduced by the period 136 for switching from DL to UL and by the necessary TA. In conditions with rising TA, the TA will reduce the effective DL transmission time in this subframe significantly. A drawback of this approach is that resources cannot be allocated to other UEs during the times of no DL transmission due to the TA and switching.
Similarly, for the UL-DL switch, a reserved period for UE switching between transmit and receive is provided by timing advance means for the UE transmitting in subframe n 134 and receiving in subframe n+1 132. As the TA affects the transmission in subframe n 134 to stop before the boundary of the subframe 132, the switching period 138 can effectively use the TA, and increasing TA will not negatively impact the UL transmission efficiency.
The current working assumption is that a UE operating in an LTE radio cell will operate either in a full-duplex or a half-duplex FDD mode. Several solutions have been contemplated in the prior art to allow for both full-duplex and half-duplex operation in wireless transmission systems. For example, U.S. Pat. No. 6,665,276 to Culbertson, et al. issued Dec. 16, 2003 and entitled “Full duplex transceiver” discloses an RF front end to an IF generator and post-processor whereby the IF generator output is variable. The transceiver up-conversion path includes an IF Filter, the output of which is input to a mixer with the output of a fixed Phase Locked Oscillator (PLO). The mixer output is input to a band-pass filter and amplified. With a single antenna configuration, the amplifier output connects to either an internal or external diplexer that interfaces to the antenna. With a dual antenna configuration, the amplifier output interfaces directly to the antenna. Similarly, the down-conversion path includes an internal or external diplexer in the single antenna configuration, a band-pass filter, a RF amplifier, a mixer that receives the RF amplifier output and the fixed PLO as inputs, an IF Filter, IF amplifier, and an attenuator for interfacing to the IF post-processor. A user-interface allows RF TX and RX frequency selection, data rate selection, and configurable options including internal or external diplexer, internal or external oscillator reference, and TX amplifier keying to allow simplex, half duplex, or full duplex communication.
U.S. Pat. No. 7,197,022 to Stanwood, et al. issued Mar. 27, 2007 and entitled “Framing for an adaptive modulation communication system” discloses a system and method for mapping a combined frequency division duplexing (FDD) Time Division Multiplexing (TDM)/Time Division Multiple Access (TDMA) downlink subframe for use with half-duplex and full-duplex terminals in a communication system. Embodiments of the downlink subframe vary Forward Error Correction (FEC) types for a given modulation scheme as well as support the implementation of a smart antennae at a base station in the communication system. Embodiments of the system are also used in a TDD communication system to support the implementation of smart antennae. A scheduling algorithm allows TDM and TDMA portions of a downlink to efficiently co-exist in the same downlink subframe and simultaneously support full and half-duplex terminals. The algorithm further allows the TDM of multiple terminals in a TDMA burst to minimize the number of map entries in a downlink map. The algorithm limits the number of downlink map entries to not exceed 2n+1, where n is the number of DL PHY modes (modulation/FEC combinations) employed by the communication system.
U.S. Pat. No. 7,339,926 to Stanwood, et al. issued Mar. 4, 2008 and entitled “System and method for wireless communication in a frequency division duplexing region” discloses a method and system for using half-duplex base stations and half-duplex nodes in a Frequency Division Duplexing region to provide wireless connectivity between the half-duplex base stations and customers in multiple sectors of a cell. The method and system can use two physical channels to form two logical channels. Each logical channel shares both physical channels during alternating frames of time. The half-duplex nodes can include a millimeter-wave band frequency synthesizer configured to transmit and receive on different channels to and from the half-duplex base station. Re-use patterns of the physical channels are used for deployment of half-duplex base stations and half-duplex nodes in the FDD region to minimize co-channel interference and interference due to uncorrelated rain fade. Additional methods and systems utilize full-duplex base stations and smart antenna to communicate with the half-duplex nodes.
United States Patent Publication No. 20070054625 to Beale published Mar. 8, 2007 and entitled “Compatible broadcast downlink and unicast uplink interference reduction for a wireless communication system” discloses embodiments that reduce interference from a mobile station (UE) uplink transmission to a received broadcast downlink transmission through a network-based scheduling of time-slotted downlink broadcast transmissions, so that they do not occur concurrently with uplink transmissions. UEs are designed and built to use: (i) downlink broadcast transmissions that are time-slotted; (ii) UEs operate either in half-duplex mode for transmission and reception of unicast services, or in full duplex mode where additional bandpass or additional highpass filtering can be applied to the DL unicast carrier; (iii) when unicast services are active for a UE, the UE informs the network of the broadcast services that are being decoded; and (iv) the network schedules unicast transmissions, broadcast transmissions, or both unicast and broadcast transmissions such that the uplink unicast transmission to a UE is never time-coincident with the broadcast transmissions to that UE.
Despite the foregoing, the prior art fails to provide an adequate solution for dynamic switching capability between full-duplex and half-duplex operation in wireless transmission systems (such as cellular networks), such that the respective advantages of both modes can appropriately be utilized. Therefore, improved apparatus and methods for the adaptive operation of full-duplex and half-duplex FDD modes in a cellular system such as LTE is needed.
Such apparatus and methods would also ideally include a UE that may support both FDD modes, so that it can be adaptively switched between full-duplex and half duplex FDD operation, rather than statically assigning modes of operation. In addition, it would advantageously further support additional modes of operation for half-duplex operation, and allow a UE to operate in a battery-efficient half duplex FDD mode as well as improve cellular data throughput.
Further, such improved apparatus and methods would allow the network to opt to switch the UE transceiver mode to optimize data scheduling as well as network resource utilization.